ITM: don't test reserved bits in is_fifo_ready #227
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On ARMv7-M, bits 31:1 of the value read from STIMx are reserved, so comparing them against zero is a bad idea. On ARMv8-M, bit 1 has been repurposed to indicate DISABLED. This means that the is_fifo_ready impl hangs forever when ITM is disabled on a Cortex-M33 (for example). Changed to test only the FIFOREADY bit on ARMv7-M, and to test either FIFOREADY or DISABLED on ARMv8-M.
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Jan 12, 2022
227: Hide trampolines from docs r=jonas-schievink a=korken89 Closes #226 Co-authored-by: Emil Fresk <[email protected]>
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This is a follow up to the discussion in #219, capturing the conclusion by @cbiffle and @adamgreig there: to indicate that the ITM FIFO is ready on FIFOREADY (only) on ARMv7-M (only) and to indicate the FIFI is ready on either FIFOREADY or DISABLED on ARMv8-M. ITM has been tested and verified on an ARMv7-M CPU (an STM32F407, a Cortex-M4) and an ARMv8-M CPU (an LPC55S69, a Cortex-M33).
Without this fix, any use of ITM will hang on ARMv8-M -- which may in fact be the root cause of #74...